§ 85. ALBUMINOIDS OR PROTEIN COMPOUNDS. 117 



Quantitative estimation. — Convert it into glucose by 

 digesting its solution about 2 hours with a little sulphuric 

 acid, and then determine the glucose with the standard 

 cupric solution. 



10 c.c. of the solution correspond to 0.05 grm. of 

 lactose. 



ALBUMINOIDS or PROTEIN COMPOUNDS. 



85. Some of these substances are soluble in water, 

 others are insoluble. Most metallic salts precipitate them 

 from their solutions, or coagulate the solutions, as it is 

 termed. 



All of them are dissolved by boiling concentrated hy- 

 drochloric acid, and the solution takes a violet color if 

 access of air is allowed. 



All of them are colored yellow by concentrated nitric 

 acid, and by iodine. 



They are colored red by a solution of mercuric nitrate 

 (Millon's test) ; this is the most delicate test for these 

 bodies ; albumen, dissolved in 100,000 parts of water, 

 may be detected by this reagent. 



If a small quantity of an albuminous substance is treat- 

 ed with dilute potassic hydrate, one or two drops of a 

 dilute solution of cupric sulphate added, and more potassa 

 until the mixture is alkaline, and the whole is well mixed 

 together, a violet precipitate appears, which dissolves after 

 a little agitation ; in the presence of a carbo-hydrate, as 

 sugar or starch, the color is bluish, and the blue tint is 

 deeper, the more of the carbo-hydrate is mixed with the 

 albuminoid. {Journal fur Prakt. Chemie, 102, 376.) 



When heated, these substances give off the odor of 

 burnt horn or hair. 



Distinctive r^dL^tim^.— Albumen is precipitated when 

 its neutral solutions are heated to 70° C, or the solution is 

 coagulated ; if alkaline, the solution needs to be neutral- 



